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Lower/Higher Tolerance Ratings for Caps?

  1. Sep 2, 2010 #1
    I built an Arduino board from scratch and I am dying to test it out, but I have nothing to hook it up to my computer with. I have a spare Serial port on the back of my computer, but since Serial uses 10V, I need to build a very simple circuit that converts the 5V from the Arduino to the 10V for the RS-232/Serial port on my computer. I need 4 1uF caps. I am going to be using ceramic...but something that I never looked at whenever I built an electronic, was the tolerance rating. Odd, yes, but its true.

    Better now than never I suppose...So, in general, is it better for a capacitor to have a tolerance of +/- 1% or +/- 5% or +/- 20%. What does tolerance really mean to me and to the application?

    Thanks.
     
  2. jcsd
  3. Sep 3, 2010 #2
    Tolerance is the variation in the component's printed value. So with a tolerance of +-20%, your 1uF capacitor could be 20% higher or lower than it actually says. So you'd want the lowest tolerance as you can but in many situations it doesn't matter too much so you can get away with cheaper but less precise parts.

    I'm not sure exactly what you're doing so I cant say exactly what tolerance you should choose, but do some calculations, would having your parts deviate by 20% or so affect the outcome by any large degree?
     
  4. Sep 3, 2010 #3
    Real RS232 is (usually) a +/-5v swing, see the Wiki page for more. Your Arduino has "logic level" serial, which is a 5/0v swing. You need a level and voltage converter like the MAX232 to do the job: http://www.kmitl.ac.th/~kswichit/MAX232/MAX232.htm [Broken]

    Which, now that I look at the circuit and there's 4 caps, is maybe what you are doing...

    The value of the caps is probably fairly advisory, so you can likely use 10-20% w/o trouble. Also you could try plugging the logic level into your computer and see if it cares. It's within the specs of real RS232 and it might just adjust to it.
     
    Last edited by a moderator: May 4, 2017
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